1. Field of the Invention
The present invention relates to the field of wireless networks.
2. Discussion of Related Art
It is well known that in a mobile communication system, the mobile terminal needs to update its location to the network. More specifically, in order to conserve signaling between the network and the mobile terminal and to reduce power drain on the mobile terminal, the mobile terminal only updates the network about its location when it crosses a paging area boundary, which is far less frequent than when it crosses a communication area (covered by a base station or radio access point) boundary.
There have been several methods proposed and studied recently to solve the paging problem in an IP-based wireless network. One proposal is described in the IP paging document located at http://www.ietf.org/rfc/rfc3132.txt. The proposal regards whether Mobile IP can support location of a mobile terminal in a dormant mode for two cases: 1) networks of radio links having a homogeneous radio technology and 2) networks of radio links having heterogeneous radio technologies. The proposal states that the signaling involved in Mobile IP is not enough to provide support for locating a dormant mode mobile terminal, especially when the one paging area includes several subnets. Since the mobile terminal does not stop in one subnet (say the subnet X) where a binding update message of Mobile IP was transmitted, the mobile terminal in the dormant mode may move into a new subnet (say the subnet Y) where the IP address is supposed to be changed. Therefore, without any support, the access router or foreign agent in the subnet X drops the packet which is destined to the mobile terminal. The only way to get the packet to the mobile terminal from the access router or foreign agent is for the mobile terminal to send the binding update message of Mobile IP to the access router or foreign agent when the mobile terminal wakes up in the new subnet Y.
Note that subnets constitute the unit of signaling for presence in Mobile IP. When a mobile node moves from one subnet to another, Mobile IP signaling is required to change the mobile terminal's care-of address (CoA). This signaling establishes the mobile terminal's presence in the new subnet. In contrast, paging areas constitute the unit of signaling for a dormant mode mobile terminal presence at the radio level. Paging area registrations or heuristics are used to establish a dormant mode mobile terminal's presence in a particular paging area.
In current mobile communication systems, the issue of finding a mobile terminal is treated as follows. The network keeps track of the location of every attached mobile terminal with the accuracy of a geographical location area (LA) that is the same as the paging area. For example, in 3GPP packet switching network, the home location register will track the mobile terminal based on the current attached SGSN (serving GPRS support node). A location update in the database takes place whenever an attached mobile terminal crosses the boundaries of a location area. Whenever an incoming call arrives, the network has to locate the called mobile terminal within the precision of a cell, i.e., to determine the base station via which a wireless signaling link between the mobile terminal and the network can be established. During paging, a specific message is broadcast simultaneously via all base stations over the whole location area so as to find out the called mobile terminal. Upon receiving the paging request, the mobile terminal responds to the base station with the stronger received signal strength. So, in this case, the paging area is equal to the location area.
In general, the mapping between paging areas and subnets can be arbitrary, but for the purpose of discussion will be considered initially to have a smooth subset relationship, in which paging areas are subsets of subnets or vice versa. As described above, the problem is that the mobile terminal when in the dormant mode does not wake up when crossing between subnets within a paging area and will not send the binding update message of Mobile IP. Since the IP paging was not solved by the process described in the document, the process was not explored further in the document.
Due to the router maximum capability, the subnet size is limited so that one paging area may include several subnets. When the dormant mode mobile terminal crosses the paging area boundary, the dormant mode mobile terminal will not send the binding update message of Mobile IP. Therefore, the router will not know the exact location of the dormant mode mobile terminal. Consequently, the location detection for the dormant mode mobile terminal is fully dependant on the L2 paging scheme.
A paging scheme is important for receiving the phone call. Because of a battery saving mode in a mobile communications system, the mobile terminal will go to the sleeping or dormant mode most of time. Once a call has arrived, a mobile terminal is paged through the paging channel.